Common problems with Wire EDM and how to avoid them
Wire EDM is a spark erosion process that cuts a profile with a thin travelling wire in deionised water. It is used for cutting hardened material, sharp internal corners and parts with no cutting force. This entry explains what it is, what the numbers on a data sheet mean, and what to put on a drawing.
It is written from the point of view of the buyer and the drawing office: the values that are realistic in production, the ones that cost money, and the way the result is verified. Where an industry sets the requirement, robotics is used as the example: repeatability across a family of near identical parts.
The problems that actually occur
These are the failures that show up on a real job, listed in the order in which they are usually discovered.
- The wire breaking on a tall part because the flush is poor. The cause is usually upstream: a datum that is not the functional one, a fixture that does not repeat, or a specification that cannot be measured the way it is written.
- Assuming a sharp internal corner is free: the wire has a radius. The cause is usually upstream: a datum that is not the functional one, a fixture that does not repeat, or a specification that cannot be measured the way it is written.
What causes them
In most cases the cause is upstream of the operation, not in it. The wire breaking on a tall part because the flush is poor is usually a symptom of one of the three causes above rather than a problem in its own right.
How they are prevented
Prevention is duller than diagnosis. Allow the wire radius on internal corners, or design a relief, and the result is confirmed by optical comparator and surface roughness gauge before the batch is released.
| Item | Note |
|---|---|
| Failure | the wire breaking on a tall part because the flush is poor |
| Prevention | allow the wire radius on internal corners, or design a relief |
| Tolerance to hold | ±0.005 mm |
| Finish to check | Ra 0.4 µm with one skim pass |
Applications
Wire EDM is used for cutting hardened material, sharp internal corners and parts with no cutting force, and in practice it appears most often in punch and die work, hardened gauges, prototype laminations, medical cutting tools.
How it fits into a machining route
Wire EDM is one operation in a sequence: roughing to leave even stock, any stress relieving the geometry needs, semi finishing, then the finishing operation that holds the tolerance. The order is what keeps the result stable as the machine warms up and the batch runs.The route is fixed before the first part is cut, and it is the route rather than the individual setting that holds the result: cutting area and the number of skim passes. Where a drawing calls for something the route cannot hold economically, that is raised at quotation rather than after the parts are made.
Standards, documentation and what is issued
The documentation requirement is in-house approval with dimensional reports. Material is supplied against a certificate where the application calls for it, inspection results are recorded with the job, and the records are kept so that a repeat order can be compared with the first instead of being measured from scratch.
Optical comparator and surface roughness gauge is the verification step. Where a customer format or a standard report is required, it is agreed before the batch starts, because a report written after the event is a report nobody can use.
Frequently asked questions
What tolerance should be specified for Wire EDM?
±0.005 mm is realistic in production. Tightening it beyond the functional requirement increases cost without improving the part.
Which material is usually used?
D2 tool steel is the usual choice, supplied against in-house approval with dimensional reports.
How is the result verified?
Optical comparator and surface roughness gauge, with the results recorded so a repeat order can be compared with the first.
What is the most common mistake?
Assuming a sharp internal corner is free: the wire has a radius.
How long does it take and what does it cost?
A realistic cycle is 1 to 8 hours depending on height, and the cost driver is cutting area and the number of skim passes.
Related capability
If you are specifying Wire EDM on a drawing and want a second opinion on the route, send the model and the quantity. The first response is a manufacturability review with the likely risk points and a quotation, so the decision can be made on facts rather than on a price alone.
Machining, inspection and documentation are handled in one place, which is why the dimensional report and the material certificate arrive with the parts rather than after them.
Related entries
These entries sit next to Wire EDM in the encyclopedia: Thread Milling, Deep Hole Drilling, 304 Stainless Steel. Reading them together gives a fuller picture of how the process, the material and the measurement affect each other.
